AGPO:
I suppose justifying the pricing depends on what context you are going to use the minis.
1) The Pure Painter: For this guy the White Lions/Pheonix Guard are a rip off - yes £25 is justified for that many hours entertainment, but he can get the same number of little plastic artworks to entertain him at half the price if he buys a different unit.
2) The Gaming Club Member: For this guy we must look from an army-wide perspective. Assuming he goes to a gaming club to hang out with his mates and play competitive games, then putting together a new army is far more expensive than say, a Sky Sports subscription for your lads’ night, not to mention the time it takes to put it together/collect a playable force. If it’s casual strategy gaming, then Napoleon: Total War is only marginally more expensive than a single box, for an infinite variety of scenarios and armies.
3) The Tournament Player: This is the only guy for whom making special units more expensive than core makes sense. Even so, this guy will play about three tournaments a year, and will have a new army each year. Not really great value.
4) The All-Round Hobbyist: For this guy, an army is a long term investment. A new unit will be added to existing armies every so often, giving him many hours of painting pleasure which produces something he can game with. £50 say for a unit of 20 Pheonix Guard is not unreasonable in this situation.